The present invention relates generally to the utilization of lignocellulosic biomass, and in certain embodiments to processes useful for liquefaction of lignocellulosic biomass for utilization of sugars derived therefrom in fermentation or other processes.
As further background, increasing emphasis has been placed in recent years upon finding ways to utilize lignocellulosic biomass to make useful products, such as fuel products. In one field of interest, fuel ethanol has been produced by fermentation of biomass feedstocks derived from plants. Currently, fuel ethanol is commercially produced from feedstocks of cornstarch, sugar cane and sugar beets. These materials, however, find significant competing uses in the food industry, and their expanded use to make fuel ethanol is met with increased prices and disruption of other industries. Alternative fermentation feedstocks and viable technologies for their utilization are thus highly sought after.
Lignocellulosic biomass feedstocks are available in large quantities and are relatively inexpensive. Such feedstocks are available in the form of agricultural wastes such as corn stover, corn fiber, wheat straw, barley straw, oat straw, oat hulls, canola straw, soybean stover, grasses such as switch grass, miscanthus, cord grass, and reed canary grass, forestry wastes such as wood, e.g. aspen wood and sawdust, and sugar processing residues such as bagasse and beet pulp. Cellulose from these feedstocks is converted to sugars, which are then fermented to produce the ethanol.
A difficulty in using lignocellulosic feedstocks is that the useful sugar content of the biomass is largely caught up in natural polymers such as cellulose and hemicellulose, and conditions or agents must be used to convert those polymeric substances to simple sugars. For this reason, research has focused upon methods for processing lignocellulosic biomass to create process feeds containing simple sugars. Some such research has been directed to pretreating lignocellulosic biomass to enhance the susceptibility of the cellulose to conversion to sugars. Such pretreatment processes are designed to break the lignin seal protecting the cellulose and to disrupt the crystalline structure of the cellulose. A variety of pretreatment methodologies have been explored for this purpose; including physical processes such as size reduction, steam explosion, liquid hot water, irradiation, cryomilling, and freeze explosion; and chemical processes such as acid hydrolysis, buffered solvent pumping, alkali or alkali/H2O2 delignification, solvents, ammonia; and microbial or enzymatic methods.
Despite previous efforts relating to processing lignocellulosic biomass feedstocks and their ultimate use in the production of ethanol, needs remain for improved and alternative biomass utilization processes, including in the production of ethanol or other useful substances from fermentation. In certain of its aspects, the present invention is addressed to these needs.